In spite of multiple modes of treatment, colon cancer remains a most common malignant disease in this country. The present investigations seek to biologically and chemically characterize cell surface antigens, not only distinctive of this malignancy, but also capable of eliciting immune, destructive responses in man. Using morphological, chemical, virological, and chemical tools, the applicant and his colleagues have described characteristic surface membrane differences between malignant and normal colon cells. Three surface membrane components of approximate molecular weights 45,000; 58,000 and 60,000 appear to be distinctive of the malignant state. Employing a two dimensional electrophoretic analysis with a first dimensional separation by charge (isoelectric focusing), and a second dimension by molecular weight, the distinctive components have been isolated for precise chemical characterization. Adequate amounts of material are available from the applicant's own colon cancer cell strains, which have been demonstrated to contain pure colon epithelial cells by morphology, much production, desmosomes, specific markers (CEA, T antigen, CSA), and to represent malignant elements by unlimited growth, lack of contact inhibition, morphology, karyology, cloning on monolayers, and outgrowth in conditioned xenogeneic hosts. The distinctive proteins were shown to bind rabbit heteroantisera capable of killing only malignant, and not normal cells. The proposed investigations not only intend to precisely characterize the chemical nature of the distinctive proteins, but also to determine whether patients afflicted with colon cancer develop immune reactions toward them in the course of their disease, by the capacity of soluble materials to trigger blastogenesis and/or to inhibit lymphocyte-mediated cytotoxicity toward colon cancer cells. Since failure to respond to the distinctive proteins may indeed play a role in the progression of the disease, spleen cells from normal individuals will be immunized in vitro with tumor cells, and then tested for their interactions with the soluble antigens. These studies may thus provide insight into unique membrane antigens on colon cancer cells which might be exploited for the development of immunodiagnostic tools or immunotherapeutic treatment modalities to improve the survival of patients with this cancer.